1. Field of Invention
The invention relates generally to a power-up procedure for a microprocessor and, more specifically, to a procedure that utilizes a standard JTAG interface to enable a computer's debugger to control the microprocessor immediately upon power-up without the use of an in-circuit emulator.
2. Background
A microprocessor starts executing commands immediately upon power-up. In a production system, a boot programmable read only memory (PROM) boots-up the system in a safe, controlled manner. In a development system, however, the boot PROM is usually also under development. Consequently, it is replaced by random access memory (RAM) into which a test boot code is loaded after power-tip. Instructions are usually fetched from the RAM starting at fixed address, e.g., zero. The microprocessor has no indication of whether the instruction stream constitutes a valid program or just random bits from uninitialized RAM memory. Thus, to avoid execution of random instructions out of uninitialized RAM immediately upon power-up, the development system must ensure that the processor remains in a controlled state. In an in-circuit emulator (ICE) environment, this problem can be solved by additional hardware. However, if tests must be performed in a production device where an ICE cannot be connected, extra pins would be necessary, which might require a new production part. Therefore, a need exists for a procedure to power-up a microprocessor without requiring additional hardware and/or dedicated pins. The present invention fulfills this and other needs.